title: Asymmetric synthesis of polyhydroxylated pyrrolizidines via transannular iodoamination with concomitant N-debenzylation.
abstract: The doubly diastereoselective "matched" conjugate addition of lithium (R)-N-but-3-enyl-N-(α-methyl-p-methoxybenzyl)amide to tert-butyl (4S,5R,E)-4,5-O-isopropylidene-2,7-dienoate (derived from d-ribose in 3 steps) and in situ enolate oxidation with (-)-camphorsulfonyloxaziridine was followed by ring-closing metathesis with Grubbs I to give a hexahydroazocine scaffold. Subsequent treatment with I(2) resulted in transannular iodoamination accompanied by loss of the α-methyl-p-methoxybenzyl group to give the corresponding pyrrolizidine scaffold as a single diastereoisomer upon direct crystallization from the crude reaction mixture. Further functional group manipulations enabled the preparation of (-)-7a-epi-hyacinthacine A1.
authors.affiliation: Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK.
authors.forename: E Anne
authors.initials: EA
authors.lastname: Brock
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Davies
authors.forename: James A
authors.initials: JA
authors.lastname: Lee
authors.forename: Paul M
authors.initials: PM
authors.lastname: Roberts
authors.forename: James E
authors.initials: JE
authors.lastname: Thomson